How to automate a script execution on import actions?
Blender doesn't have these kinds of hooks, the closest thing you can get to this is to write your own operator that runs import, then your own code afterwards.

For Python importers you could customize the script to include your own functionality and in a few causes you could monkey patch the importer scripts. But basically this isn't supported.

See this question for more details:
Run additional code after user has executed and finished an operator